Oil dampers or squeeze film dampers surround the bearing of a rotating shaft with an oil filled annulus. The annulus is supplied with pressurized oil and is defined between a stationary structural support and a radially inward bearing housing while being contained by forward and aft piston rings. The oil damper accommodates radial movement of the shaft, bearings and bearing housing relative to the stationary support where radial movement is caused by shaft imbalance conditions.
Ideally the pressurized oil flows one way from the oil inlet, purges the oil filled annulus and flows out under pressure through restricted gaps about the piston rings. As the shaft rotates under an imbalanced condition, a positive pressure is created in the oil filled annulus in advance of the eccentrically rotating shaft (as the radial dimension of the annulus is squeezed) and a negative pressure follows the eccentrically rotating shaft (as the radial dimension of the annulus increases).
The negative oil pressure relative to ambient gas pressure can draw gas into the oil filled annulus. Gas intrusion into the oil filled annulus through the piston ring gaps can affect the effectiveness of the oil damper. Gas bubbles can explosively collapse under positive pressure causing cavitation erosion of adjacent metal surfaces. Gas bubbles can also degrade the oil density and the capacity of the pressurized oil film to support loads with the oil filled annulus. Improvement is thus desirable.